1. Field of the Invention
The present invention relates to a method for manufacturing an antenna. Moreover, the present invention relates to a method for manufacturing a semiconductor device having an antenna.
2. Description of the Related Art
In recent years, development of a semiconductor device which can send and receive data wirelessly has been actively carried out. Such a semiconductor device is also referred to as an IC tag, an ID tag, an RF (radio frequency) tag, an RFID (radio frequency identification) tag, a wireless tag, an electronic tag, a wireless processor, a wireless memory, a wireless chip, or the like.
A wireless chip generally includes an antenna and an IC chip. The IC chip is formed using an element layer having a transistor and the like provided over a silicon wafer.
As one of characteristics required for an antenna of a wireless chip, there is low resistance of an antenna (a wiring) itself. The Q-value has been generally known as a parameter for evaluating an electric characteristic of an antenna, and is represented by a general formula: Q=ωL/R. In the general formula, ωL represents reactance of a coil and R represents electric resistance of the antenna. According to this general formula, it is apparent that the Q value is inversely proportional to resistance (R) of the antenna, and the Q value is increased as the resistance (R) is reduced. The higher the Q value is, the longer a communication distance of a wireless chip is. Therefore, there is a concern that as increasing the resistance (R) of an antenna, the Q value is reduced, which results in reduction in a communication distance.
As a means for reducing resistance of an antenna, it is desired that a line space (a width between lines) of a wiring used as an antenna is prevented from widening. As a method for forming a wiring used as an antenna, after forming a conductive film, the conductive film is subjected to patterning to form the antenna (for example, see patent document 1). Further, in this specification, “patterning” indicates treatment by which an object is etched into a desired shape.    Patent Document 1: Japanese Patent Application Laid-Open No. 2004-220591
When, after forming a conductive film by sputtering, a method for patterning the conductive film using a mask made from a resist is used, a line space can be set to be about 10 μm. However, this method has problems that since the mask made from a resist is used, the number of steps for forming an antenna is increased so that lots of processing time is required. In addition, manufacturing cost is also increased with increasing the number of steps and processing time.
In a case of a droplet discharging method using an ink-jet technique, processing time required for forming an antenna is shorter than a case of using a method using a mask made from a resist; however, a limit of a line space is about 50 μm so that resistance of the antenna is increased. Note that the droplet discharging method is a method by which a droplet (also, referred to as a dot) of a composition containing a material for a conductive film, an insulating film, or the like is selectively discharged (injected) to form a film in a predetermined position, and this method is also referred to as a dot method.
In a case of using screen printing, as compared with a method using a mask made from a resist, processing time required for forming an antenna is shortened as well as the case of using the droplet discharging method. However, a limit of a line space in the case of using screen printing is about 50 to 100 μm so that the resistance of the antenna is also increased. In particular, in a case of forming an antenna using a printing plate, in which an antenna pattern is formed in advance, the printing plate must be designed in consideration of the amount of a running resin. Therefore, it has been necessary to secure enough space between lines of an antenna.
As mentioned above, when processing time required for forming an antenna is shortened, a line space of the antenna is increased by the conventional method. Accordingly, a width of an antenna cannot be sufficiently widened and resistance of the antenna is increased; and therefore, it has been difficult to improve a communication distance. Further, in a case of forming a loop antenna as an antenna, the sufficient winding number cannot be secured so that it has been difficult to manufacture a semiconductor device with a sufficient communication distance.